1. Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to a device and a driving method thereof including a panel with a built-in touch panel and a method of driving the same.
2. Discussion of the Related Art
With the advance of various portable electronic devices such as mobile communication terminals, smart phones, tablet computers, notebook computers, and etc., the demand for flat panel display (FPD) devices applicable to the portable electronic devices is increasing. Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, organic light emitting display devices, etc. are being actively researched as the FPD devices.
A touch panel is a type of input device that is included in display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs), and enables a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
Particularly, the demand of display devices with in-cell type touch panel, which include a plurality of built-in elements configuring the touch panel for slim portable terminals such as smart phones and tablet Personal Computers (PCs), is recently increasing.
In an in-cell type display device, as disclosed in U.S. Pat. No. 7,859,521, a plurality of common electrodes for display are segmented into a plurality of touch driving areas and touch sensing areas. An in-cell type display device allows a mutual capacitance to be generated between the touch driving area and the touch sensing area. Thus, the in-cell type display device measures the change in a mutual capacitance that occurs in touch to determine whether there is a touch.
In other words, in the related art in-cell type display device, a plurality of common electrodes for displaying an image perform the function of a touch electrode when a panel operates in a touch sensing mode, for simultaneously performing a display function and a touch function.
As described above, in a related art in-cell type mutual capacitive display device using the common electrode, the common electrode is used as a driving electrode or a receiving electrode that is used for touch sensing. An image display period and a touch sensing period are separated. Thus, noise generated in the image display period does not affect touch sensing.
In the image display period, a driving electrode and a receiving electrode act as common electrodes. In the touch sensing period, a periodic driving pulse is applied to the driving electrode, and a touch IC determines whether there is a touch by using a sensing signal that is received through the receiving electrode.
FIG. 1 is a waveform diagram showing an image display period and a touch sensing period in a related art in-cell type display device, and FIG. 2 is an exemplary diagram showing waveforms of a voltage outputted to a driving electrode and a receiving electrode in a related art in-cell type display device.
A touch panel applied to an in-cell type display device includes a touch electrode to which common voltage is supplied during the image display period and driving voltage is supplied during touch sensing period, and a receiving electrode to which common voltage is supplied during the image display period and reference voltage is supplied during the touch sensing period.
In a related art in-cell touch type display device, as shown in FIG. 1, an image display period (Display) and a touch sensing period (Touch) are separated from each other.
During an image display period, as shown in FIG. 2, a common voltage Vcom is supplied to the driving electrode TX and the receiving electrode RX. During a touch sensing period, a driving voltage Vd having a pulse type is supplied to the driving electrode TX, and a reference voltage Vref is supplied to the receiving electrode RX.
In this case, block dim is caused in a panel of the in-cell type display device due to a difference between root mean square values Vrms of voltages respectively supplied to the driving electrode TX and the receiving electrode RX during the touch sensing period.
That is, as shown in FIG. 2, in the image display period, common voltages Vcom having the same level are supplied to the driving electrode TX and the receiving electrode RX, and thus, an equal voltage is generated for the driving electrode TX and the receiving electrode RX, whereby an image-quality defect such as block dim due to a luminance difference between the electrodes is not caused.
However, in a touch sensing period (Touch), because the driving voltage Vd supplied to the driving electrode TX swings between the common voltage Vcom and a voltage greater than the common voltage Vcom, the root mean square value of the driving voltage Vd is greater than the reference voltage Vref (or the common voltage Vcom) supplied to the receiving electrode RX. Therefore, block dim is caused due to a luminance difference between the driving electrode TX and the receiving electrode RX.